**2. Origin of digestate**

For protection of the environment, the recycling of organic materials has essential role. The anaerobic digestion (AD) is an important method to decrease the quantity of organic wastes by utilization them for energy and heat production. The by-product of this process is the digestate.

In an AD process, different organic materials could be used alone or in mixture of animal slurries and stable wastes, offal from slaughterhouse, energy crops, cover crops and other field residues, organic fraction of municipal solid wastes (OFMSW), sewage sludge. The quality of digestate as a fertilizer or amendment depends not only on the ingestates but also on the retention time. The longer retention time results in less organic material content of the digestate because of the more effective methanogenesis (Szűcs et al., 2006).

Biogas technology is known to destroy pathogens. The thermophilic AD increases the rate of elimination of pathogenic bacteria, therefore the amounts of fecal coliforms and enterococcus fulfilled the requirements of EU for hygienic indicators (Paavola & Rintala, 2008). Mesophilic digestion alone may not be adequate for correct hygienization, it needs a separate treatment (70 oC, 60 min., particle size<12 mm) before or after digestion, especially in the case of animal by-products (Bendixen, 1999; Sahlström, 2003).

acidification.

agricultural use.

Type of ingestate

Liquid cattle

Energy crops, cow manure slurry and agro-industrial waste

Energy crops, cow manure slurry, agroindustrial waste and OFMSW

Cow manure, plant residues and offal

Clover/grass or pea straw or cereal straw or silage maize and clover/grass silage (mean)

**3.2 Macroelement content of digestate** 

Type of digestion process

slurry mesophilic 4.27

thermophilic <sup>105</sup>

thermophilic <sup>110</sup>

mesophilic and thermophilic

mesophilic

Total-N

(% DM)

(g kg-1 TS)

(g kg-1 TS)

0.2013 (%m/m, fresh matter)

0.253 (%m/m, fresh matter)

Table 2. Characteristics of liquid digestates from different origin

Digestate: A New Nutrient Source – Review 297

The alkaline pH of digestate is a useful property because of the worldwide problem of soil

The other characteristics of digestate also are differed depending on the source materials and the digestion process. In Table 2 some major properties of different liquid digestates can be seen, but these are mean values which could be altered in the course of the digestion process. Therefore regular monitoring of digestate properties is needed in the case of its

Swine manure mesophilic 2.93 (g L-1) 2.23 (g L-1) 0.93 (g L-1) 1.37 (g L-1) *Loria* 

52.9 (‰ Nt)

2.499 (g L-1)

2.427 (g L-1)

0.157 (%m/m, fresh matter)

0.176 (%m/m, fresh matter)

Nitrogen (N) is a major plant nutrient and is the most common plant growth limiting factor of agricultural crops. The fertilizing effect of added N is decreased by the inadequate synchrony of crop N demand and soil N supply (Binder et al., 1996; Möller & Stinner, 2009). The advantage of digestate application is the possibility of reallocation of the nutrients within the crop rotation from autumn to spring, when crop nutrient demand arises (Möller

(Nt) NH4-N Total-P Total-K Source of

0.66 (% DM)

10.92

11.79

274.5 mg kg-1 (fresh matter)

0.62 (% DM)

4.71 (% DM)

(g kg-1 TS) - *Pognani* 

(g kg-1 TS) - *Pognani* 

736.45 mg kg-1 (fresh matter)

18.5 (% DM) data

*et al., 2007* 

*Möller et al., 2008* 

*et al., 2009* 

*et al., 2009*

*Makádi et al.,2008b* 

*Stinner et al., 2008* 

Two types of digestate are the liquid and the solid ones which are distinguished on the bases of their dry matter (DM) content. The liquid digestate contains less than 15% DM content, while the solid digestate contains more than 15% DM. Solid digestate can be used similar to the composts or could be composted with other organic residues and can be more economically transported over grater distances than the liquid material (Møller et al., 2000).
